internal variable for units setting (g20/21)?

This is probably a silly question, but I'll ask anyway.

Is there any internal variable that stores the current units setting that a program is running in?

I'm asking because i'm creating a custom toolchange-probe subroutine, and I'm using some inch values (my machine also defaults to inches), so my subroutine issues a G20(just to be safe). If the calling file is running under G21, then I'd set back to G21 before exiting the subroutine, if not, then leave it at inches.

It's not critical, since i can add the line manually since i'm editing the file anyway, more of a little nice-to-have, to make the code a little cleaner.

thanks.

#<_metric> - Return 1 if G21 is on, else 0.
#<_imperial> - Return 1 if G20 is on, else 0.

you sir, are awesome.
thank you.

just found an even more elegant way. M73
Haven't tested it yet, but it sounds like it will do exactly what I want. Save state, and return to original settings at the end of the subroutine.

a subroutine shoudt always be filled with the mashine units
if it is presented to a libary like here in the Forum
First line #UNITS in ****
so people using it can detact

or you go for a Factor in First hand so only factor is to set